Coal is the only fossil fuel in the United States available in sufficient abundance to provide an increasing share of this country's energy requirements over the next 20 years. To utilize coal's energy it must be converted to energy-rich liquids/gas by a variety of industrial processes. All coal conversion technologies currently available generate polycyclic hydrocarbons as chemical by-products that have toxic and mutagenic effects in diverse biological systems including the human body. One such compound, benzo(a)pyrene is known to be carcinogenic/mutagenic in a variety of experimental systems. The toxic and mutagenic effects of exposure to such chemicals are worrisome and the long-term hazards of exposure relates at least in part to their ability to interact with cellular DNA. Workers in occupations associated with exposure to soot and to coal combustion products clearly have an increased incidence of skin cancer. Virtually nothing is known about the toxicity, mutagenicity and the DNA-modifying activity of most of the polycyclic hydrocarbons produced in industrial coal conversion processes. Systematic studies are planned to evaluate the effects of a defined series of polycyclic hydrocarbons on drugs and carcinogen metabolism in the skin of experimental animals, and in cultured human skin fibroblasts and keratinocytes. Studies are also planned to evaluate the DNA-modifying potential of the polycyclic hydrocarbons generated in coal conversion processes. The biochemical interaction between these chemicals and the genetic material of prokaryotic and eukaryotic cells will be assessed in order to more precisely define the genetic risks associated with occupational exposure to these agents. New knowledge obtained from these studies could lead to the identification of specific polycyclic hydrocarbons with toxic and/or mutagenic effects. It might then be possible to reduce exposure to these agents and thereby reduce the occupational hazards of coal conversion processes.